This newborn pigmy hippopotamus at Rotterdam’s Blijdorp Zoo is no bigger than a head of lettuce! An adult pigmy hippo is just over three feet tall (91 cm), just one-fifth of the size of the common hippopotamus, and it is the only other species of hippo in the world. Reclusive and nocturnal, the pigmy hippo is semi-aquatic and needs to live near water to keep its skin moisturized and its body cool.